This invention relates to a surface-mounting capacitor, which is usable as a noise filter, a bypass capacitor or a decoupling capacitor on an electronic substrate.
Recently, with the improvements in performance, advances in miniaturization and/or weight reduction of electronic components mounted on an electronic substrate, a power supply is rapidly miniaturized. The miniaturization of the power supply is firstly achieved by increasing of the operating frequencies of the electronic components. The high operating frequencies of the electronic components cause a problem of electromagnetic interference in circuits on the electronic substrate. Accordingly, demands increasingly become severe regarding performance of a component, such as a noise filter, mounted on the electronic substrate. To meet the demands, a solid electrolytic capacitor has been developed which has conductive functional polymer film as a cathode and a valve effect metal layer, such as an aluminum or tantalum layer, as an anode, and has been in practical use as a surface-mounting thin type capacitor. Such a solid electrolytic capacitor is disclosed in Japanese Unexamined Patent Application Publications No. JP2002-313676 A (hereinafter referred to as Document 1), No. JP2002-164760 A (hereinafter referred to as Document 2), or No. JP2005-39040 A (hereinafter referred to as Document 3).
According to Document 1, a first conventional solid electrolytic capacitor has a first metal plate. The first metal plate has oxide films on both faces thereof and a pair of anode portions at both ends thereof. The first metal plate is sandwiched by flat cathode members of functional polymer to expose the anode portions. The cathode members are covered with second metal plates at opposite sides of the first metal plate. The anode portions are connected to anode terminals while one of the second metal plates is connected to a cathode terminal. The other of the second metal plates projects from ends of the cathode members over the anode portions. With this structure, the noise reduction performance of the first conventional capacitor is improved at high frequency range over 100 MHz.
Document 2 discloses a second conventional solid electrolytic capacitor having a distribution constant circuit portion. The second conventional capacitor is similar to the first conventional capacitor except that it has a metal layer instead of the second metal plates to form the distribution constant circuit portion. The metal layer covers the flat cathode members and the part of the first metal plate sandwiched by the flat cathode members. With this structure, the second conventional capacitor can reduce noise over a wide band.
Document 3 discloses a third conventional solid electrolytic capacitor having a main element similar to the first conventional capacitor except that the second metal plates are substantially the same size. The third conventional capacitor further has reinforcing metal plates and thermosetting adhesive impregnated tapes for fixing the reinforcing metal plates to the main element. The reinforcing metal plates have steps to reduce intervals between edges thereof. The steps prevent oxygen from penetrating to the main element and thereby the third conventional capacitor has high reliability and high heat resistance.
At any rate, the conventional capacitors have the two anode portions each. The anode portions are located at both sides of the cathode member(s). Accordingly, the anode terminals connected to the anode portions are located at both sides of the cathode terminal connected to the cathode member. To use the conventional capacitor as a two terminal type capacitor, the anode terminals must be electrically connected to each other. Generally, a connecting wire (or pattern) to connect the anode terminals each other is formed on the electronic substrate on which the capacitor is mounted. The connecting wire is so arranged to avoid a land for the cathode terminal that a land pattern including the land and the connecting wire is larger than that of a three terminal type capacitor. Therefore, the conventional capacitors mentioned above have a common problem that different land patterns having different occupying areas are necessary in accordance with intended use. That is, the size of a mounting area for mounting each conventional capacitor on the electronic substrate must be varied according to the intended use of the capacitor.
In addition, there is a problem that masking process and removing process are necessary to mask the anode portions by mask layers and to remove the mask layers in a manufacturing process for each conventional capacitor. This is because the second metal plates (or a metal layer) are located between the anode portions.